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Axle configuration solver

The inverse question. You have a weight and a length and no rig: which axle configurations clear the federal bridge formula? Ranked, with a to-scale diagram for each and the whole thing in the URL.

The load

Gross weight is everything on the ground — tractor, trailer and freight. Outer wheelbase is the distance from the front axle to the rearmost axle, which is the L the bridge formula uses. It is not the trailer length and it is not the overall length of the combination.

Both inputs are in the address bar, so this result is a link you can send. There is no script on this page.

Common wheelbases

Four, so the grid wraps two by two and none is ever left alone on a line. Each is a link that keeps the weight you have typed, which is also why these are links and not buttons — a button cannot be a URL.
60 ft outer wheelbase100 ft outer wheelbase140 ft outer wheelbase180 ft outer wheelbase
Configurations that clear the formula

12 of 12 tested

10,000 lb over 8 ft of outer wheelbase, every axle count from 2 to 13.

2 axles Recommended — fewest axles that clear

Clears · 0 lb left on the binding group, axles 1–2

8 ftAxle 1 — 0 ft from the steer axle, 5,000 lb5k1Axle 2 — 8 ft from the steer axle, 5,000 lb5k2
Open this rig in the axle weight checker
3 axles

Clears · 0 lb left on the binding group, axles 1–3

4 ft4 ftAxle 1 — 0 ft from the steer axle, 3,300 lb3.3k1Axle 2 — 4 ft from the steer axle, 3,300 lb3.3k2Axle 3 — 8 ft from the steer axle, 3,400 lb3.4k3
Open this rig in the axle weight checker
4 axles

Clears · 0 lb left on the binding group, axles 1–4

2.67 ft2.66 ft2.67 ftAxle 1 — 0 ft from the steer axle, 2,500 lb2.5k1Axle 2 — 2.67 ft from the steer axle, 2,500 lb2.5k2Axle 3 — 5.33 ft from the steer axle, 2,500 lb2.5k3Axle 4 — 8 ft from the steer axle, 2,500 lb2.5k4
Open this rig in the axle weight checker
5 axles

Clears · 0 lb left on the binding group, axles 1–5

2 ft2 ft2 ft2 ftAxle 1 — 0 ft from the steer axle, 2,000 lb2k1Axle 2 — 2 ft from the steer axle, 2,000 lb2k2Axle 3 — 4 ft from the steer axle, 2,000 lb2k3Axle 4 — 6 ft from the steer axle, 2,000 lb2k4Axle 5 — 8 ft from the steer axle, 2,000 lb2k5
Open this rig in the axle weight checker
6 axles

Clears · 0 lb left on the binding group, axles 1–6

1.6 ft1.6 ft1.6 ft1.6 ft1.6 ftAxle 1 — 0 ft from the steer axle, 1,700 lb1.7k1Axle 2 — 1.6 ft from the steer axle, 1,700 lb1.7k2Axle 3 — 3.2 ft from the steer axle, 1,700 lb1.7k3Axle 4 — 4.8 ft from the steer axle, 1,700 lb1.7k4Axle 5 — 6.4 ft from the steer axle, 1,700 lb1.7k5Axle 6 — 8 ft from the steer axle, 1,500 lb1.5k6
Open this rig in the axle weight checker
7 axles

Clears · 0 lb left on the binding group, axles 1–7

1.33 ft1.34 ft1.33 ft1.33 ft1.34 ft1.33 ftAxle 1 — 0 ft from the steer axle, 1,400 lb1.4k1Axle 2 — 1.33 ft from the steer axle, 1,400 lb1.4k2Axle 3 — 2.67 ft from the steer axle, 1,400 lb1.4k3Axle 4 — 4 ft from the steer axle, 1,400 lb1.4k4Axle 5 — 5.33 ft from the steer axle, 1,400 lb1.4k5Axle 6 — 6.67 ft from the steer axle, 1,400 lb1.4k6Axle 7 — 8 ft from the steer axle, 1,600 lb1.6k7
Open this rig in the axle weight checker
8 axles

Clears · 0 lb left on the binding group, axles 1–8

1.14 ft1.15 ft1.14 ft1.14 ft1.14 ft1.15 ft1.14 ftAxle 1 — 0 ft from the steer axle, 1,300 lb1.3k1Axle 2 — 1.14 ft from the steer axle, 1,300 lb1.3k2Axle 3 — 2.29 ft from the steer axle, 1,300 lb1.3k3Axle 4 — 3.43 ft from the steer axle, 1,300 lb1.3k4Axle 5 — 4.57 ft from the steer axle, 1,300 lb1.3k5Axle 6 — 5.71 ft from the steer axle, 1,300 lb1.3k6Axle 7 — 6.86 ft from the steer axle, 1,300 lb1.3k7Axle 8 — 8 ft from the steer axle, 900 lb9008
Open this rig in the axle weight checker
9 axles

Clears · 0 lb left on the binding group, axles 1–9

1 ft1 ft1 ft1 ft1 ft1 ft1 ft1 ftAxle 1 — 0 ft from the steer axle, 1,100 lb1.1k1Axle 2 — 1 ft from the steer axle, 1,100 lb1.1k2Axle 3 — 2 ft from the steer axle, 1,100 lb1.1k3Axle 4 — 3 ft from the steer axle, 1,100 lb1.1k4Axle 5 — 4 ft from the steer axle, 1,100 lb1.1k5Axle 6 — 5 ft from the steer axle, 1,100 lb1.1k6Axle 7 — 6 ft from the steer axle, 1,100 lb1.1k7Axle 8 — 7 ft from the steer axle, 1,100 lb1.1k8Axle 9 — 8 ft from the steer axle, 1,200 lb1.2k9
Open this rig in the axle weight checker
10 axles

Clears · 0 lb left on the binding group, axles 1–10

0.89 ft0.89 ft0.89 ft0.89 ft0.88 ft0.89 ft0.89 ft0.89 ft0.89 ftAxle 1 — 0 ft from the steer axle, 1,000 lb1k1Axle 2 — 0.89 ft from the steer axle, 1,000 lb1k2Axle 3 — 1.78 ft from the steer axle, 1,000 lb1k3Axle 4 — 2.67 ft from the steer axle, 1,000 lb1k4Axle 5 — 3.56 ft from the steer axle, 1,000 lb1k5Axle 6 — 4.44 ft from the steer axle, 1,000 lb1k6Axle 7 — 5.33 ft from the steer axle, 1,000 lb1k7Axle 8 — 6.22 ft from the steer axle, 1,000 lb1k8Axle 9 — 7.11 ft from the steer axle, 1,000 lb1k9Axle 10 — 8 ft from the steer axle, 1,000 lb1k10
Open this rig in the axle weight checker
11 axles

Clears · 0 lb left on the binding group, axles 1–11

0.8 ft0.8 ft0.8 ft0.8 ft0.8 ft0.8 ft0.8 ft0.8 ft0.8 ft0.8 ftAxle 1 — 0 ft from the steer axle, 900 lb9001Axle 2 — 0.8 ft from the steer axle, 900 lb9002Axle 3 — 1.6 ft from the steer axle, 900 lb9003Axle 4 — 2.4 ft from the steer axle, 900 lb9004Axle 5 — 3.2 ft from the steer axle, 900 lb9005Axle 6 — 4 ft from the steer axle, 900 lb9006Axle 7 — 4.8 ft from the steer axle, 900 lb9007Axle 8 — 5.6 ft from the steer axle, 900 lb9008Axle 9 — 6.4 ft from the steer axle, 900 lb9009Axle 10 — 7.2 ft from the steer axle, 900 lb90010Axle 11 — 8 ft from the steer axle, 1,000 lb1k11
Open this rig in the axle weight checker
12 axles

Clears · 0 lb left on the binding group, axles 1–12

0.73 ft0.72 ft0.73 ft0.73 ft0.73 ft0.72 ft0.73 ft0.73 ft0.73 ft0.72 ft0.73 ftAxle 1 — 0 ft from the steer axle, 800 lb8001Axle 2 — 0.73 ft from the steer axle, 800 lb8002Axle 3 — 1.45 ft from the steer axle, 800 lb8003Axle 4 — 2.18 ft from the steer axle, 800 lb8004Axle 5 — 2.91 ft from the steer axle, 800 lb8005Axle 6 — 3.64 ft from the steer axle, 800 lb8006Axle 7 — 4.36 ft from the steer axle, 800 lb8007Axle 8 — 5.09 ft from the steer axle, 800 lb8008Axle 9 — 5.82 ft from the steer axle, 800 lb8009Axle 10 — 6.55 ft from the steer axle, 800 lb80010Axle 11 — 7.27 ft from the steer axle, 800 lb80011Axle 12 — 8 ft from the steer axle, 1,200 lb1.2k12
Open this rig in the axle weight checker
13 axles

Clears · 0 lb left on the binding group, axles 1–13

0.67 ft0.66 ft0.67 ft0.67 ft0.66 ft0.67 ft0.67 ft0.66 ft0.67 ft0.67 ft0.66 ft0.67 ftAxle 1 — 0 ft from the steer axle, 800 lb8001Axle 2 — 0.67 ft from the steer axle, 800 lb8002Axle 3 — 1.33 ft from the steer axle, 800 lb8003Axle 4 — 2 ft from the steer axle, 800 lb8004Axle 5 — 2.67 ft from the steer axle, 800 lb8005Axle 6 — 3.33 ft from the steer axle, 800 lb8006Axle 7 — 4 ft from the steer axle, 800 lb8007Axle 8 — 4.67 ft from the steer axle, 800 lb8008Axle 9 — 5.33 ft from the steer axle, 800 lb8009Axle 10 — 6 ft from the steer axle, 800 lb80010Axle 11 — 6.67 ft from the steer axle, 800 lb80011Axle 12 — 7.33 ft from the steer axle, 800 lb80012Axle 13 — 8 ft from the steer axle, 400 lb40013
Open this rig in the axle weight checker
Scope

What this answers, and where the answer stops

It is a feasibility probe on federal geometry, not a specification for a truck.

What it covers

Every axle count from 2 to 13 against 23 U.S.C. §127(a) — each candidate's full set of consecutive-axle groups, the 20,000 lb single-axle limit, the 34,000 lb tandem cap and the 34-34-at-36-ft exception.

What it does not cover

Whether a tractor can be built that puts axles where the model puts them; any state’s own axle or gross limits; permit fees; escorts; and seasonal restrictions. A configuration that clears here can still be illegal in a specific state on a specific road in March.

What it costs

Nothing, no account, and no JavaScript. Both inputs are in the query string and the whole page is server-rendered, so it works with scripting disabled and the result is a shareable link.

How it works

Three steps, in order

One candidate per axle count

For each axle count the solver builds the evenly spaced, evenly loaded layout over the outer wheelbase you gave it, with the rounding residue landing on the last axle so the gross stays exactly the number you typed.

Every group of every candidate gets checked

The same engine the axle weight checker uses, so a candidate here and the same rig there cannot disagree. Each candidate reports the group with the least headroom, because that is the group that decides.

Ranked, fewest axles first

Passing configurations come first, cheapest rig first; the rest are ranked by how close they came. The fewest-axle pass is marked recommended with an outline, and each row links into the forward tool with that layout preloaded.

Why this one

Two things that make the answer trustworthy

A "no" here is a real no

The modelled layout is the optimum for a fixed weight, length and axle count: even spacing gives every group the longest span it can have, even loading gives every group the lightest weight it can have, and the per-axle limit is minimised in its maximum at the same time. So the even layout maximises the slack on whichever constraint binds.

That is what makes a failure conclusive rather than suggestive. If 13 axles over that wheelbase cannot carry the load, no arrangement of 13 axles can — the fix is more outer wheelbase, not more axles. The invariant is asserted against randomised perturbations in the test suite rather than taken on trust.

Axle counts tested
2–13
Candidates evaluated
12
Clearing the formula
12

The result is a link

Both inputs live in the query string, so a configured result can be bookmarked, sent to a carrier and reopened unchanged. The length presets are anchors rather than buttons for exactly that reason.

And every candidate carries a link into the axle weight checker with its own layout already encoded, so the step from "this many axles would work" to "is my actual rig legal in Ohio" is one click and no retyping.

Federal single axle
20,000 lb
Federal tandem axle
34,000 lb
Federal gross weight
80,000 lb
FAQ

Questions

Does this tell me which truck to buy?

No. It reports the minimum number of axles the federal bridge formula requires for that weight across that outer wheelbase, using an evenly spaced, evenly loaded layout. Real tractors cannot put axles at arbitrary positions, so each row links into the axle weight checker with the layout preloaded — edit it to the rig you actually have and re-check.

Why is "no configuration passes" a reliable answer?

Because the modelled layout is the best case. For a fixed weight, length and axle count, even spacing gives every axle group the longest span it can have and even loading gives every group the lightest weight it can have, so it maximises the slack on whichever constraint binds. If the even layout fails at N axles, no arrangement of N axles over that length passes — the load needs more outer wheelbase, not more axles.

What about the 34-34 tandem exception?

It is the one geometry even spacing cannot reach, so it is evaluated separately. 23 U.S.C. §127(a)(3) lets two consecutive tandem sets each carry 34,000 lb when their outer axles are at least 36 ft apart — 68,000 lb where the bare formula allows only 66,000 — so at four axles the solver tests the two-tandem arrangement as well and keeps whichever clears.

Does a passing configuration mean no permit?

Only below 80,000 lb. The bridge formula governs how weight is distributed; 23 U.S.C. §127(a) separately caps an unpermitted Interstate vehicle at 80,000 lb gross. Above that every configuration here needs an overweight permit, and the axle weight checker prices it against the issuing state’s own published schedule.